You might try editing the embed code a bit. YouTube and Vimeo have been removing the http: from their video codes so they work better on sites that use http: or https:
See if this works for you:
<iframe width="480" height="302" src="//www.ustream.tv/embed/recorded/48161748?v=3&wmode=direct" scrolling="no" frameborder="0" style="border: 0px none transparent;"></iframe>
I’m not sure if UStream is set up to accommodate that, but it might be worth a shot. If that doesn’t help, we may need to check with their support and see if they have an idea as to why it’s displaying black instead of your video.